BlackBerry said demand for the app is "amazing." About 6 million people have signed up for information about BBM on the company's website.

"In just seven hours, about one million Android users were using the unreleased version of BBM for Android," BlackBerry wrote. "What you don't know is that more than one million people have found creative ways to 'side load' BBM on their iPhone. This is incredible."

To make for a smoother rollout this time, BlackBerry has implemented a "simple line-up system" granting access to the app on a first-come-first-serve basis. Visit BBM.com from your Android or iPhone browser and install the app. When you open it for the first time, you'll need to enter your email address to "hold your spot in line," and BlackBerry will then email you when it's your turn to start using BBM.

Those who already signed up at BBM.com can start using the app immediately, without waiting. "If you didn't sign up in advance, don't worry — we are focused on moving millions of customers through the line as fast as possible," BlackBerry said.

BlackBerry first announced a free version of BBM for Android and iOS in May, and an Android beta followed in early August. Several weeks later, there were rumours that BlackBerry would spin off its BBM division into a separate business, but last month, BlackBerry said a consortium led by Fairfax Financial would acquire the company for $4.7 billion (£2.9 billion) and take it private, though other firms are reportedly eyeing BlackBerry, too.

The BBM glitch was the latest black eye for BlackBerry, which also last month announced it would cut 4,500 employees, or 40 per cent of its workforce.